1. Field of the Invention
This invention relates generally to remote monitoring systems, and in particular to remote methane monitoring systems for the purpose of detecting the presence of natural gas leaks within residential, commercial, and industrial facilities.
2. Background Art
Natural gas utility companies operate approximately 61 million customer gas meters in the United States alone, supplied by over one million miles of pipeline, 17 hundred transmission stations and 17 thousand compressors. To help maintain security and integrity of this vast distribution system, the natural gas utility industry installs volume correctors and electronic data recorders at compressor stations, metering stations, step-down stations and meter vaults, for example, which provide trend data about the functionality of the distribution system. A volume corrector is typically installed with a gas meter. The volume corrector accurately measures the pressure and temperature of the gas and corrects the volume flow estimation from the gas meter using ideal gas law calculations. Similarly, an electronic data recorder accurately measures pressure and temperature and stores the information. Both types of instruments communicate the stored results to the utility company using proprietary supervisory control and data acquisition (SCADA) systems modulated over plain old telephone service (POTS).
Gas pipelines are also subject to regular inspections to detect leaks. Routine periodic leak surveys are costly, and it is estimated that the natural gas distribution and transmission industry spends over $300 million annually to survey the pipeline network for leaks. Moreover, because gas leaks may occur at appliances or within interior distribution piping on the consumer side of the gas meter, utility pipeline surveys are of limited effect.
Gas explosions due to leakage and accumulation of natural gas in end-user buildings are an unfortunate and too frequent occurrence. Currently, like smoke detectors, heat detectors, carbon monoxide detectors and water sensors, there exists several types of discrete natural gas sensors that may be installed in homes or commercial buildings that notify occupants when there is a predetermine minimum concentration natural gas in the atmosphere. Such natural gas detectors are typically stand-alone alarms that sound a warning when triggered so that the occupants may safely evacuate. However, some models include relay contacts so that they can be wired into a central alarm or home security system. A security monitoring service may then notify authorities in the event an alarm is triggered.
Natural gas detectors may rely on varying detection methods and principles. For example, combustible gas indicators (CGIs) work on the principles of catalytic combustion and thermal conductivity of a gas sample and thus sense virtually all combustible gases. CGIs are low-sensitivity devices that are generally unable to detect gas mixtures much below the lower combustible concentration limit. A more sensitive leak detector commonly used is the flame ionization detector (FID). The FID operates on the principle of measuring the ionic concentration produced in a flame burning carbon compounds. Like the CGIs, FIDs sense hydrocarbon gases. While the CGI typically measures gas concentration in percentage, the FID typically measures gas concentration in parts per million (ppm). The CGI and FID both typically use an extractive sample or measurement path. In this method, target gas concentration is measured by a detector installed in a measurement chamber through which gases of interest are continually drawn from the immediate surrounding atmosphere.
The optical methane detector (OMD™) operates by absorption of infrared (IR) light by methane. Because natural gas primarily contains methane gas, detection of methane gas serves for detection of natural gas. It is a well known spectroscopic principle that gas molecules absorb energy in narrow bands (sometimes referred to as absorption lines) surrounding specific wavelengths in the electromagnetic spectrum. For example, methane has strong absorption bands at 1.33 μm, 1.66 μm, 3.3 μm, and 7.6 μm. At wavelengths falling even slightly outside the narrow absorption band, there is essentially no absorption. Thus, an OMD measures the attenuation of an infrared light source passing through a gas sample at the methane-characteristic absorption wavelength to determine the presence of methane gas. An OMD is more selective than either a CGI or a FID, because it measures methane specifically and not all combustible gases. OMDs generally use a short open path sample method, which eliminates the sampling time delay associated with extractive sampling method of CGIs or FIDs. In a short open path configuration, the light source is transmitted across a line of sight and is either reflected to an optical detector by a fixed reflector of known characteristics located only a short distance from the light source or the light is received directly by a fixed detector located only a short distance away from the light source. OMD sensitivity in detecting methane is of the same order of magnitude as a FID.
A laser methane detector is a prior-art device that operates on the same absorption spectroscopy principle as an OMD but uses a rapidly and specifically-tunable wavelength-modulated diode laser as a light source. By sweeping the laser wavelength between a non-absorption band and a particular absorption band of a target gas molecule and monitoring the reflection measurements during the wavelength sweeps, both the background transmittance over the laser beam's path and the concentration of target gas molecules integrated within the laser beam's path can be accurately determined. A laser methane detector is thus well-suited for utility company pipeline surveys, because a fixed sample chamber is not required and accurate measurements can be made over long and widely-varying path lengths.
However, CGIs, FIDs, OMDs, and laser detectors are generally considered to be too expensive to be widely accepted for home use and thus find limited use, typically in potentially hazardous industrial locations. Current sensors widely used in home natural gas detectors are based on electrochemical catalytic semiconductors, whose electrical properties are altered in the presence of various hydrocarbon gases. These sensors are inexpensive, but they have significant performance limitations. Electrochemical catalytic semiconductors are unstable, prone to drift, and subject to false alarms due to moisture or household chemicals. The sensors, which are easily contaminated by household chemicals, have a relatively short life span. Additionally, there is no practical way for the home owner to test the calibration and functioning of the detector. As a result, the homeowner is at risk that the methane sensor may frequently trigger false alarms or may not alarm at all when a detectable hazardous condition is present.
Although state and federal safety commissions are increasingly urging the use of natural gas monitors, there is currently little utility company monitoring of detectable atmospheric gas levels at the end-user locations. Low cost electrochemical semiconductor methane sensors are too prone to false alarms, and more reliable detectors have been too expensive to deploy. Perhaps a more significant barrier has been the lack of a low cost reliable infrastructure through which a multitude of methane detectors can communicate back to the utility company.
If reliable methane monitors are widely deployed at a gas utility company's end-user locations and each monitor automatically notifies the gas utility company of actual pending dangers, proactive steps may be taken by the utility company to alleviate the danger before a catastrophe occurs.
3. Identification of Objects of the Invention
Therefore, a primary object of the invention is to provide a cost-effective system and method for utility-provider-monitoring of actual atmospheric gas levels at various distribution system and end-user locations, including residential, commercial and industrial buildings.
Another object of the invention is to provide a methane detector that uses Smart Energy™ communication networks for compatibility, rapid deployment, and low cost.
Another object of the invention is to provide a method and apparatus for monitoring natural gas levels that provides the ability to monitor the gas level at a remote installation.
Another object of the invention is to provide a method and sensor for monitoring natural gas levels in which the functioning of the sensor can be automatically or remotely tested and calibrated, and if not working properly, notification can automatically be provided to the end-user and to the gas company.
Another object of the invention is to provide a method and sensor for monitoring natural gas levels in which the results of sensor self-tests are further analyzed to project the need for service.
Another object of the invention is to provide a method and sensor for monitoring the atmosphere in remote locations in which carbon monoxide gas and natural gas levels may be present.
Another object of the invention is to provide a volume corrector with integrated methane detector that communicates with a gas utility company.
Another object of the invention is to provide an electronic data recorder with integrated methane detector that communicates with a gas utility company.
Another object of the invention is to provide a fire alarm with integrated methane detector that communicates with a gas utility company.